Dextromethorphan particularly in its hydrobromide salt is a demonstrated safe and effective non-narcotic cough suppressant for the temporary relief of coughing. Dextromethorphan hydrobromide is available in a wide variety of cough and cough/cold medications. Dextromethorphan hydrobromide is available as a sole ingredient in cough medication by itself or with other active ingredients. Dextromethorphan hydrobromide is also available in a cough control lozenge form from various manufacturers which have a dosage of 5.0 milligram of dextromethorphan hydrobromide per lozenge. Such lozenqes are in candy form and comprise corn syrup solids and sugar as major ingredients. However, incorporating dextromethorphan hydrobromide into lozenges is highly troublesome because dextromethorphan has a bitter taste an anesthetic mouth-feel and an unpleasant after-taste. In fact it is very difficult to effectively mask the taste of dextromethorphan at concentrations of greater than 2.0 milligrams per lozenge with sweeteners or flavors.
To incorporate more than 2.0 milligrams of dextromethorphan hydrobromide in lozenges the dextromethorphan hydrobromide is generally provided as a 10% adsorbate onto magnesium trisilicate. The adsorbate form provides efficient taste masking to produce an acceptably palatable lozenge form. This adsorbate, which releases the dextromethorphan hydrobromide at the lower pH of the stomach fluids renders the active ingredient almost tasteless in the mouth. Unfortunately, ten times the weight of dextromethorphan hydrobromide adsorbate must be added to achieve an equivalent dosage of dextromethorphan hydrobromide.
Additionally, as reported by David Peters in volume 1 of Pharmaceutical Dosage Forms: Tablets, (3 volume 2nd ed. Herbert A. Lieberman, Leon Lachman and Joseph B. Schwartz. New York: Marcel Dekker, 1989) dextromethorphan hydrobromide adsorbate is insoluble and has a melting point above that of the lozenge's candy base. Therefore, the adsorbate can not be readily incorporated into a candy base. The adsorbate when incorporated into a candy base normally produces a grainy, rough lozenge texture with an unpleasant mouth feel.
To over come this problem the standard solution is to prepare the adsorbate as a granulation of the dextromethorphan hydrobromide adsorbate with either glycerin or propylene glycol. A ratio of one part solvent to three parts dextromethorphan hydrobromide produces a free flowing granulation. Although lozenges made by the above described process can be easily flavored and have a smooth feel, the addition of the adsorbate in this manner limits the amount of dextromethorphan hydrobromide in each lozenge to a dose of 10 milligrams or less. The effective amount of dextromethorphan typically provided in a lozenge is in the range of 5.0 to 7.5 milligram per lozenge unless a large lozenge (4.0 grams) is produced.
Thus, it appears that dextromethorphan hydrobromide cannot readily be incorporated into medicated candy lozenges without special steps being taken. Its successful incorporation into candy bases usually requires a granulation with either glycerin or propylene glycol and an large quantity of inactive material which provides a lozenge with a maximum dosage of 5.0 to 7.5 milligrams per lozenge for an approximately 4.0 gram lozenge product.
The present invention solves these problems by adding the dextromethorphan hydrobromide adsorbate in a liquid suspension into the candy feed prior to the formation of a candy base. The addition of the dextromethorphan adsorbate into the candy feed also dispenses with the need to form a granulation of dextromethorphan adsorbate with glycerin or propylene glycol. These and several other objects and advantages of the present invention will be described in the following sections of this specification.